This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
The acquisition of 4D light-field data), which can be viewed as a sampling of a 4D light field (i.e. the recording of light rays as explained in FIG. 1 of the article: “Understanding camera trade-offs through a Bayesian analysis of light field projections” by Anat Levin and al., published in the conference proceedings of ECCV 2008) is an hectic research subject.
Indeed, compared to classical 2D images obtained from a camera, 4D light-field data enable a user to have access to more post processing features that enhance the rendering of images and/or the interactivity with the user. For example, with 4D light-field data, it is possible to perform with ease refocusing of images a posteriori (i.e. refocusing with freely selected distances of focalization meaning that the position of a focal plane can be specified/selected a posteriori), as well as changing slightly the point of view in the scene of an image. In order to acquire 4D light-field data, several techniques can be used. Especially, a plenoptic camera, as depicted in document WO 2013/180192 or in document GB 2488905, is able to acquire 4D light-field data. Details of the architecture of a plenoptic camera are provided in FIGS. 1, 2, 3, 4 and 5 of the present document.
In the state of the art, there are several ways to represent (or define) 4D light-field data. Indeed, in the Chapter 3.3 of the Phd dissertation thesis entitled “Digital Light Field Photography” by Ren Ng, published in July 2006, three different ways to represent 4D light-field data are described. Firstly, 4D light-field data can be represented, when recorded by a plenoptic camera as the one depicted in FIG. 1 for example, by a collection of micro-lens images (see the description of FIG. 2 in the present document). 4D light-field data in this representation are named raw images (or raw 4D light-field data). Secondly, 4D light-field data can be represented, by a set of sub-aperture images. A sub-aperture image corresponds to a captured image of a scene from a point of view, the point of view being slightly different between two sub-aperture images. These sub-aperture images give information about the parallax and depth of the imaged scene (see the description of FIG. 7 for more details). Thirdly, 4D light-field data can be represented by a set of epipolar images (see for example the article entitled: “Generating EPI Representation of a 4D Light Fields with a Single Lens Focused Plenoptic Camera”, by S. Wanner and al., published in the conference proceedings of ISVC 2011).
However, it should be noted that a device that can acquire 4D light-field data such as a plenoptic camera, may have some optical aberrations on the main lens. Among optical aberrations one distinguishes: spherical aberrations, astigmatism, coma, lateral chromatic aberrations, axial chromatic aberrations, etc. Therefore, these optical aberrations degrade the quality of images derived from the acquired 4D light-field data.
One solution to overcome this issue is described in the article: “Digital Correction of Lens Aberrations In Light Field Photography” by Ren Ng and Pat Hanrahan. In this article, using a plenoptic camera the authors propose to compute a shift correction parameter using photon propagation through the real lenses versus photon propagation versus an ideal thin lens approximating the real lens. More precisely, the shift correction parameter corresponds to the ray correction function that is obtained from ray tracing differences between an ideal ray space (based on an ideal lens modeling) and an aberrated ray space. Thus, the technique proposed in this article relies on a precise knowledge of all the optical elements (shape, material) which define the main-lenses, and is based on ray tracing technique.
The proposed technique in this document does not need to have such sharp knowledge of all the elements of the main-lenses for obtaining a shift correction parameter.